1. Field of the Invention
This invention relates generally to processes for labeling containers and particularly to a process for making labeled containers using a stretch blow molding process.
2. Description of the Prior Art
A number of different labeling techniques are common to the bottle industry. One of the most common, particularly in the carbonated soft drink industry, is glue-on labels. These are flat decorated/labeled films that are wrapped around a bottle and glued on one edge.
Another more common labeling technique used to label extrusion blow molded containers is “in-mold” labeling. For this method, the printed label (typically made of paper or plastic film) is placed into the blow mold just prior to the parison being inflated. The heat of the hot parison as it contacts the label and mold wall causes the label to stick to the bottle, often with the assistance of a heat sensitive adhesive. Examples of this technology are described in U.S. Pat. No. 6,004,682, U.S. Pat. No. 5,980,233, and U.S. Pat. No. 5,753,278.
Another more recent development is the use of shrink fit or “contour” labels. These labels are made by printing on oriented film stock. The film is made into the shape of a tube (typically by solvent bonding one edge), placed over the container, and “heat-shrunk” around the bottle. The heat-shrinking is usually performed in a heat tunnel where the temperature is hot enough to cause the oriented label to shrink around the container. Upon passing through the heat tunnel. the oriented film/label will shrink to fit the shape of the container. The film takes the shape of the container by “form-fitting” to the container. The label is usually printed using a distortion printing process. This process effectively compensates for the final change in dimensions of film and inked pattern.
This heat shrinking, contour-fitting process can be performed using a variety of different polymers as long as the film is properly oriented. These include, but are not limited to, polyesters and copolyesters, polyvinyl chloride (PVC), polyolefins (polyethylene, polypropylene, etc), polyamides and polystyrene. It is important, however, that the temperature used to shrink the film, usually just below the glass transition temperature (“Tg”) of the bottle, is low enough that the bottle does not become distorted as it passes through the shrink tunnel.
An important feature of standard contour-fitting labeling is that it requires oriented film stock. This orientation is usually induced via a tenter frame (and in some cases a machine direction orientation drafter) or a double-bubble blown film line. Both are expensive processes and add significant additional costs to methods for making and using the film. Furthermore, a shrink tunnel, which also adds cost, is required to make the oriented film shrink around the container. This extra piece of equipment also adds cost to the process.
There is, therefore, a need for less expensive and more convenient methods to apply labels to containers during the stretch blow molding process.